Rock drill

ABSTRACT

A rock drill for rotary hammers is proposed in which a conveying helix ( 3 ) having main and secondary webs ( 6  to  9 ) is used. A one-piece carbide crown, with its wing-shaped main and secondary lips ( 24  to  27 ), is butt-welded to the conveying helix.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a rock drill for hand-guarded rotary hammers,percussion drilling machines, rotary machines and the like.

The invention relates to a rock drill according to the preamble of claim1.

2. Related Art

Conventional rock drills consist of a drill shank and a drill head inwhich a carbide cutting element, roof-shaped in side view and extendingover the entire drill nominal diameter, is inserted (see, for example,DE 29 12 394 A1). In addition to this “main cutting tip”, secondarycutting tips, likewise arranged in a roof shape, may also be arranged,and these secondary cutting tips may be arranged, for example, in across shape, that is to say while including a right angle, or also in anx-shape (for example EP 0 657 617 A1). The drill head has axiallyrunning slot-shaped recesses in which such cutting tips are inserted andbrazed in place.

In order to achieve adequate endurance of the carbide tips, they musthave a certain minimum thickness, a factor which necessitates acorrespondingly wide locating slot for the carbide tips. However, such alocating slot extending over the entire diameter, and possiblytransversely thereto, for such a carbide cutting tip having main andsecondary lips reduces the available wall thickness for supporting therespective main and/or secondary lips, which is of importance inparticular in drilling tools having a smaller nominal diameter, forexample less than 10 mm. This applies in particular when the drill headis of very slim design for forming large flute cross sections fordrillings to be removed (see, for example, DE 197 34 094, FIGS. 4 and7).

In multi-start conveying helices, the drillings transport from the drillhead into the conveying helix flutes is effected by appropriate recessesin the drill head. The recesses also weaken the drill head with regardto the support of the carbide cutting tips used.

DE 197 53 731 A1 has disclosed a rock drilling tool in which, in orderto improve the conveying properties, main and secondary conveyinghelices are formed, so that, in a two-start conveying helix for example,a type of four start conveying helix is produced by the secondaryconveying web present in each case. A transversely inserted, roof-shapedcarbide cutting tip results in each case in two main conveying fluteswhich are subdivided into a plurality of secondary conveying flutes bythe secondary webs. With one secondary conveying helix in one mainconveying flute, two secondary conveying flutes are therefore formed,that is to say a total of four secondary conveying flutes in the case ofa two-start conveying helix (see, for example, FIGS. 1 and 2 of DE 19753 731 A1).

The access to each secondary conveying flute is achieved by an extremelythin drill head, which is achieved by a straight, axially parallelrunout of the conveying helix in the region of the drill head.

Drilling tools and in particular rock drills which have a drill headmade entirely of carbide have been disclosed, the drill head beingprovided with intimated drillings flutes which lead to the individualdrillings flutes in the conveying helix (DE 43 39 245 A1). Used in afurther tool in this respect according to DE 197 09 771 A1 is, forexample, a cross-shaped carbide drilling head which has main andsecondary lips, the diameter over the secondary lips being slightlysmaller than the nominal diameter of the drill. In this rock drill, theone-piece drill head of carbide can be attached with an essentially flatconnecting surface to a drill core (not shown in any more detail) bymeans of a brazed or welded joint. In this way, four drillings disposalflutes are formed.

Finally, DE 197 07 115 A1 shows a rock drill in which a star-shapedcarbide insert formed in one piece is embedded in corresponding axially[sic] longitudinal grooves in the drill head. The use of only three lipsin the exemplary embodiment of this publication permits three disposalflutes, but with corresponding weakening of the drill head at thesupporting embedding of the carbide insert.

OBJECTS OF THE INVENTION

An object of the invention is to produce an optimized rock drill whichin particular has high endurance with low friction, losses and optimumconveying properties.

SUMMARY OF THE INVENTION

The above and other objects are achieved according to an embodiment of arock drill of the present invention which is set forth herein by way ofexample only. Exemplary modifications are additionally described herein.

The invention is based on the knowledge that optimum drilling propertiescan only be achieved when conveying helix and drill head are adapted toone another according to the invention. For this purpose, the conveyinghelix must have good conveying properties, which is achieved by a largeconveying volume of the conveying flutes. However, a large conveyingvolume of the disposal flutes generally results in a small core crosssection, which leads to weakening of the drilling tool, in particular inthe region of the drill head. This applies in particular when the drillhead has one or more longitudinal slots for accommodating carbidecutting tips.

To achieve optimum conveying properties, the present invention uses arock drilling tool as disclosed by DE 197 53 734 A1 of the applicant. Asalready described above, a high conveying capacity is formed in the caseof such a drilling tool by means of a large conveying volume in largedrillings flutes, in which, however, secondary conveying helices areincorporated for assisting the conveyance of drillings and forstrengthening the drill shank. The conveying helix consequently consistsof main and secondary conveying helices which have optimum conveyingproperties.

In order to also optimize such a drilling tool in the drill head, aone-piece carbide drill head or carbide crown is attached, the geometryof which, with regard to the main lips and secondary lips, is designedin such a way that, to a very large extent, a smooth transition isproduced at the cross-sectional geometries of the main and secondarywebs of the drill conveying helix in the transition region to the drillhead. As a result, no weakening of the drill head occurs due tolongitudinal slots to be made for the main and/or secondary cuttingtips, so that, in addition to a robust drill head, optimum conveyingproperties are also ensured.

Especially advantageous is the development of the invention to theeffect that, as an alternative to a cross-shaped carbide crown, anX-shaped carbide crown may also be used, to be precise depending on thegeometrical adaptation of the main and secondary lips of the drill headto the main and secondary webs of the conveying helix. The transition ofthe drillings flutes from the conveying helix into the drill head isthus effected virtually without any hindrance; that is to say that thedrillings are removed from the drill head into the conveying helixwithout constrictions disturbing the drillings flow in the region of thedrill head. In addition, a high degree of guidance properties of thedrill head is ensured in particular during the spot drilling operation.

Furthermore, it is advantageous that the drill head has a carbide crownwith an additional centering point. As a result, the spot-drillingoperation can be improved. One or more centering lips may also beprovided.

In an exemplary embodiment, the conveying helix of the rock drill is oftwo-start design, having in each case two helically encircling main websand two secondary webs lying in between in each case. As a result, across-shaped carbide crown or also an X-shaped carbide crown can be usedfor forming main conveying flutes and secondary conveying flutes.

A further development of the invention lies in the fact that the outsidediameter of the secondary lips of the carbide crown is as far aspossible equal to or only slightly larger than the outside diameter ofthe secondary conveying helix or secondary webs of the conveying helix,whereas the outside diameter of the main carbide lip of the carbidecrown, this outside diameter forming the nominal diameter of thedrilling tool, is adapted to the outside diameter of the main webs ofthe conveying helix. In this case, the outside diameter of the secondarywebs and thus of the secondary lips is about 0.5 to 0.9 times andpreferably 0.7 to 0.8 times the outside diameter of the main webs or themain lip.

Furthermore, it is advantageous that the land widths of the main websare approximately the same as the thickness of the main lip of thecarbide crown.

Provision is made according to the invention for the conveying edges ofthe main and/or secondary webs, for forming bearing surfaces fordrillings, to preferably run approximately at right angles to the drilllongitudinal axis.

In an advantageous development of the invention, the secondary web ofthe secondary conveying helix is designed with a land which tapers to apoint and in each case leads to the conveying side of the secondary lipof the carbide crown. Other cross sectional forms may also be used forthe secondary conveying helix. Reference is made in this respect inparticular to DE 197 53 731 A1.

Further details and advantages follow from the description of theexemplary embodiment below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following with the aid of the drawingswhich showing an exemplary embodiment and without restricting thegeneral inventive idea.

FIG. 1 shows a side view of a drilling tool according to the invention,and

FIG. 2 shows a plan view of the drilling tool in an enlargedrepresentation.

DETAILED DESCRIPTION OF THE INVENTION

The rock drill 1 shown in FIG. 1 in side view consists of a drill head2, a helical shank adjoining this drill head and having a two-startconveying helix 3, and a clamping shank 4 adjoining this helical shankand intended for inserting into a drive machine. The clamping shank 4has locating means 5 for inserting into a rotary hammer (SDS-plusshank).

Identical or corresponding parts are given the same reference numeralsin the drawings and may not be introduced again.

In its construction, the helical shank or conveying helix 3 is inprinciple designed in the same way as described in the publication DE197 53 731 A1 of the applicant and in particular in FIGS. 1 and 2 there.Reference is hereby expressly made thereto. In this case, in the presentexemplary embodiment, the conveying helix 3 is designed as a two-startconveying helix, in each case a main disposal flute 10, 11 being formedover a height section h₁ between two helically encircling main webs 6,7. These height sections h₁ are only shown symbolically in FIG. 1 inorder to show the region of these main disposal flutes 10, 11. The mainwebs 6, 7 of the conveying helix 3 have an outside diameter d₁ and alsohave, for example, a rectangular or semi-trapezoidal cross section withconveying edges 12, 13 lying perpendicularly to the drill longitudinalaxis 44.

Located within each main disposal flute 10, 11 having the main webs 6, 7defining them is in each case an encircling secondary web 8, 9 having asmaller outside diameter d₂. The secondary web 8, 9 is formed as aprojection relative to the main disposal flute 10, 11. The main web 6therefore forms a lateral, approximately radially running conveying edge12 for drillings to be conveyed, and the main web 7 forms acorresponding conveying edge 13 for corresponding drillings. Equally,the secondary web 8 has a conveying edge 14 for drillings, and thesecondary web 9 has a corresponding conveying edge 15 for correspondingdrillings. It follows from this that the main disposal flute 10 isdivided into two disposal flutes 16, 17 having he conveying edges 12,14, and the further main disposal flute 11 is divided into two furtherdisposal flutes 18, 19 having the conveying edges 13, 15. The conveyinghelix is therefore a two-start conveying helix 3 having the main webs6,7 with in each case secondary web 8, 9 embedded in the drillingsdisposal flute. In addition to the conveying edges 12 to 15, which to avery large extent run radially, the conveying helix 3 has axiallyparallel sections in the flute root, which are indicated by referencenumeral 20.

The width of the main webs 6, 7 is s₁ (see FIG. 2), and the secondarywebs 8, 9 are designed in such a way that they taper virtually to apoint at their outer periphery. The diameter ratio d₁ to d₂ isapproximately d₂≈0.7 to 0.9×d₁.

Apart from that, reference is expressly made to D 197 53 731 A1 forexplaining the construction of the helical shank 3. Such a helix isproduced by a machining process for example.

The rock drill according to FIG. 1 has a one-piece carbide crown 21, asshown in FIG. 1 in side view and in FIG. 2 in a plan view of thedrilling tool.

The carbide crown 21 is designed as a carbide cross; that is to say thatthe vertical longitudinal symmetry planes 22, 23 are at right angles toone another. The carbide cross 21 has two main lips 24, 25 lying on thevertical longitudinal plane 22 and two secondary lips 26, 27 lying onthe vertical longitudinal symmetry plane 23. The main and secondary lips24 to 27 have front rake faces 29 and 30, respectively, which point inthe direction of rotation (arrow 28) of the drilling tool. Flanksections 33, 34 are located behind the respective cutting edge 31, 32.

A nominal diameter D₁ is formed by the length, shown in plan view inFIG. 2, of the two main lips 24, 25. A diameter D₂ of the two secondarylips 26, 27 is obtained from the representation in FIG. 2 in theirlongitudinal extent.

The diameter D₁ of the main lips 24, 25 is slightly larger than theoutside diameter d₁ of the main webs 6, 7. Likewise, the diameter D₂ isthe same size as or only slightly larger than the outside diameter d₂ ofthe secondary webs 8, 9. In this case, the ratio of D₂ to D₁ may beapproximately D₂≈0.7 to 0.9×D₁.

In its center, the carbide cross 21 has an additional, pyramidalcentering point 35. As can be seen from FIG. 2, the first symmetry plane36 in this case connects the cutting edges 31 of the two main lips 24,25, and the second symmetry plane 37 connects the two cutting edges 32of the two secondary lips 26, 27.

By means of a suitable joining process, such as, for example, aresistance welding process, diffusion welding process or brazingprocess, the carbide crown 21 is butt-welded with its flat bottomsurface 38 Onto an appropriately prepared top flat surface 39 of thehelical shank 3, the main lip 24 being in alignment with the main web 6and the main lip 25 being in alignment with the main web 7. For thispurpose, the thickness s₁ of the main lips 24, 25 is designed to beapproximately the same as the land width s₂ of the main webs 6, 7.Lateral front flanks 42 of the main lips 24, 25 merge into the conveyingedges 12, 13 of the conveying helix. Likewise, front flanks 43 of thetwo secondary lips 26,27 are in alignment with the conveying edges 14,15 of the secondary webs 8, 9.

The carbide crown 21, at its connecting surface 38, may have additionalcentering means or fastening means such as pins or webs or the like.

The invention ensures that the material removed by the rake faces 29, 30of the carbide crown 21 passes directly into the disposal flute 40, 41lying in front of it. The butt-welded carbide crown 21 thus results inextremely large drillings disposal flutes in front of the respectivecutting edges 31, 32 of the main and secondary lips 24, 25 and 26, 27,respectively. This results in optimum conveying properties

As can be seen by way of example from FIGS. 1 and 2, the cutting edges31, 32 are arranged in a plane 45 on which a drill longitudinal axis 44is disposed perpendicularly.

The invention is not restricted to the exemplary embodiment shown anddescribed. On the contrary, it also comprises all modifications anddevelopments within the scope of the patent claims. For example, insteadof being designed in a cross shape, the carbide crown may also bedesigned in an X-shape, an obtuse angle preferably being set between theleading main lips 24, 25 of the trailing secondary lips 26, 27.Furthermore, the diameter ratio of the diameters d₁ to d₂ of the mainand the secondary web may also vary.

The invention has been described in detail with respect to exemplaryembodiments, and it will now be apparent from the foregoing to thoseskilled in the art, that changes and modifications may be made withoutdeparting from the invention in its broader aspects, and the invention,therefore, as defined in the appended claims, is intended to cover allsuch changes and modifications that fall within the true spirit of theinvention.

LIST OF DESIGNATIONS

-   1 Rock drill-   2 Drill head-   3 Helical shank with 2-start conveying helix-   4 Clamping shank-   5 Locating means-   6 Main web-   7 Main web-   8 Secondary web-   9 Secondary web-   10 Main disposal flute-   11 Main disposal flute-   12 Conveying edge-   13 Conveying edge-   14 Conveying edge-   15 Conveying edge-   16 Disposal flute-   17 Disposal flute-   18 Disposal flute-   19 Disposal flute-   20 Axially parallel sections-   21 Carbide crown-   22, 23 Longitudinal symmetry plane-   24, 25 Main lip-   26, 27 Secondary lip-   29, 30 Front rake face-   31, 32 Cutting edge-   33, 34 Flank section-   35 Centering point-   36, 37 Symmetry plane-   38 Surface-   39 Surface-   40, 41 Disposal flute-   42, 43 Flank-   44 Drill longitudinal axis-   45 Plane

1. A rock drill having a longitudinal axis, the rock drill comprising: adrill head formed from a one-piece carbide crown, the drill head havingmain lips having a first outside lip diameter formed by a longitudinalextent of the main lips, and secondary lips having a second outside lipdiameter formed by a longitudinal extent of the secondary lips and beingset back relative to the first outside lip diameter; and one of asingle- and multi-state conveying helix having helically encircling mainwebs having a first outside web diameter that is equal to or slightlysmaller than the first outside lip diameter, and helically encirclingsecondary webs having a second outside web diameter, the main andsecondary webs having conveying edges in disposal flutes fortransporting drillings, the conveying helix being connected to the drillhead by one of a welded or brazed joint in such a manner that the mainwebs are connected to the main lips and the secondary webs are connectedto the secondary lips.
 2. The rock drill according to claim 1, whereinthe conveying edges of the main and secondary disposal flutes run outinto lateral front flanks of the main and secondary lips of the carbidecrown drill head.
 3. The rock drill according to claim 1, wherein thefirst and second outside lip diameters are one of the same size as andslightly larger than the first and second outside web diameters,respectively.
 4. The rock drill according to claim 1, wherein the mainand secondary lips form one of a cross shape and X-shape in plan view.5. The rock drill according to claim 1, wherein the carbide crown of thedrill head has one of a centering point and at least one or morecentering lips.
 6. The rock drill according to claim 1, wherein theconveying helix is of a two-start design, having two helicallyencircling main webs and two secondary webs lying in between in eachcase.
 7. The rock drill according to claim 1, wherein the first outsidelip diameter is larger than the second outside lip diameter, and thesecond outside lip diameter is approximately 0.5 to 0.9× the firstoutside lip diameter.
 8. The rock drill according to claim 1, wherein athickness of the main lips is one of approximately the same width as,slightly wider than and slightly narrower than a land width of the mainwebs.
 9. The rock drill according to claim 1, wherein the secondary webshave a land tapering to a point.
 10. The rock drill according to claim1, wherein the secondary webs have a land tapering to one of a point, aflat end, and a round end, and the secondary webs have a prominencerelative to a flute root, the prominence being one of rectangular,trapezoidal, semi-trapezoidal, triangular, crowned, and hemispherical incross section.
 11. The rock drill according to claim 1, wherein, to formbearing surfaces for drillings, the conveying edges of at least one ofthe main webs and secondary webs run approximately at right angles tothe drill longitudinal axis.
 12. The rock drill according to claim 1,wherein the carbide crown of the drill head has a connecting surfacethat is substantially flat and has at least one of centering andpositioning aids.
 13. The rock drill according to claim 1, wherein themain and secondary lips have cutting edges arranged in a plane lyingperpendicularly to the drill longitudinal axis.
 14. The rock drillaccording to claim 7, wherein the second outside lip diameter is 0.7 to0.8× the first outside lip diameter.